You can fit as many, or as few, images on a sheet of A4 as you choose because you don't have to accept the default image sizes; you can simply resize them to fit the available space. With that in mind, the easiest software to use often isn't an image-processing program but a desktop publishing one. You simply open a blank document, import one or more photos and drag the handles in the corners to resize them appropriately. Serif PagePlus Starter Edition (which is compatible with Windows 8) would be ideal for such a purpose:
http://www.serif.com/desktop-publishing-software/?mc=FSSPAGEPLUS
(Other DTP programs, such as Microsoft Publisher, can do the job just as well).
Serif also offer an excellent free image-processing program, which you might like. (It's a lot easier to get to grips with than either Photoshop or GIMP but still with plenty of flexibility. It's compatible with Windows 8):
http://www.serif.com/free-photo-editing-software/?MC=FSSPHOTOPLUS
It might also be worth taking a look at the software which came with your printer. (Many people simply install it and forget about it). For example, Canon printers are supplied with Canon Easy-PhotoPrint, which is specifically designed to allow users to print multiple images on a single sheet to their preferred dimensions.
Chris